Blur a mesh without nodes or cycles?
This does not answer your question directly, but consider this as an alternatively way to implement a more realistic atmosphere effect. (With Blender Render)

Basically, you want to use the volume material type on a sphere, this gives you much more control over the density of the atmosphere, and you can tweak the density and colour without fussing around with blurring or nodes.

The following screenshot has all the settings you need to generate the atmosphere.



Blend File